Dark Shadows: User-Level Guest/Host Linux Process Shadowing

The concept of a shadow process simplifies the design and implementation of virtualization services such as system call forwarding and device file-level device virtualization. A shadow process on the host mirrors a process in the guest at the level of the virtual and physical address space, terminating in the host physical addresses. Previous shadow process mechanisms have required changes to the guest and host kernels. We describe a shadow process technique that is implemented at user-level in both the guest and the host. In our technique, we refer to the host shadow process as a dark shadow as it arranges its own elements to avoid conflicting with the guest process's elements. We demonstrate the utility of dark shadows by using our implementation to create system call forwarding and device file-level device virtualization prototypes that are compact and simple.